The pair decay width of the first excited 0+ state in 12C (the Hoyle state) is deduced from a novel analysis of the world data on inelastic electron scattering covering a wide momentum transfer ...range, thereby resolving previous discrepancies. The extracted value Γπ=(62.3±2.0) μeV is independently confirmed by new data at low momentum transfers measured at the S-DALINAC and reduces the uncertainty of the literature values by more than a factor of 3. A precise knowledge of Γπ is mandatory for quantitative studies of some key issues in the modeling of supernovae and of asymptotic giant branch stars, the most likely site of the slow-neutron nucleosynthesis process.
The validity of the Brink-Axel hypothesis, which is especially important for numerous astrophysical calculations, is addressed for 116,120,124Sn below the neutron separation energy by means of three ...independent experimental methods. The γ -ray strength functions (GSFs) extracted from primary γ -decay spectra following charged-particle reactions with the Oslo method and with the shape method demonstrate excellent agreement with those deduced from forward-angle inelastic proton scattering at relativistic beam energies. In addition, the GSFs are shown to be independent of excitation energies and spins of the initial and final states. The results provide a critical test of the generalized Brink-Axel hypothesis in heavy nuclei, demonstrating its applicability in the energy region of the pygmy dipole resonance.
The gamma strength function and level density of 1^{-} states in ^{96}Mo have been extracted from a high-resolution study of the (pover →, pover →^{'}) reaction at 295 MeV and extreme forward angles. ...By comparison with compound nucleus γ decay experiments, this allows a test of the generalized Brink-Axel hypothesis in the energy region of the pygmy dipole resonance. The Brink-Axel hypothesis is commonly assumed in astrophysical reaction network calculations and states that the gamma strength function in nuclei is independent of the structure of the initial and final state. The present results validate the Brink-Axel hypothesis for ^{96}Mo and provide independent confirmation of the methods used to separate gamma strength function and level density in γ decay experiments.
Change in nuclei deformation leads to changes in statistical properties such as the nuclear level density (NLD) and γ-ray strength function (γSF). The NLD and γSF of 151Sm were extracted using the ...Oslo method. The strength of the scissors resonance (SR) and its centroid energy for 151Sm were found to be 2.13 ± 0.60 μN2 and 2.48 ± 0.25 MeV, respectively. These results were used to place the SR of 151Sm and its magnetic dipole strength B(M1)SR into the context of previously measured Sm isotopes.
Abstract
Extensive experimental investigations into understanding the fine structure of giant resonances in nuclei across the periodic table have been carried out in recent years using the ...state-of-the-art K600 magnetic spectrometer of iThemba LABS, Cape Town, South Africa. Based on the established results in comparison to various theoretical calculations, it has been found that the fine structure observed in different giant resonances, namely Isoscalar Giant Quadrupole Resonance (ISGQR), Isovector Giant Dipole Resonance (IVGDR) and Isoscalar Giant Monopole Resonance (ISGMR), in light nuclei such as
40
Ca,
28
Si and
27
Al is dominated by Landau damping although signatures for the role of the spreading width are also found. In this report, characteristic energy scales extracted in light nuclei are compared with the state-of-the-art theoretical calculations, while the fine structures results obtained are compared using semblance analysis to search for possible signatures of common fragmentation patterns induced by Landau damping and coupling to 2p-2h states obtained from different giant resonances.
The coupling of the giant quadrupole resonance to valence-space configurations is shown to be the origin of the formation of low-lying quadrupole-collective structures in vibrational nuclei with ...symmetric and mixed-symmetric character with respect to the proton-neutron degree of freedom. For the first time experimental evidence for this picture is obtained from electron- and proton scattering experiments on the nucleus ^{92}Zr that are sensitive to the relative phase of valence-space amplitudes by quantum interference.
Abstract
The iThemba Laboratory for Accelerator Based Sciences (iThemba LABS) is a centre of expertise and innovation in the field of nuclear-structure physics and is a leader in several high-impact ...studies. One of the highlights of these nuclear-structure experiments is the study of the broad structure of the IsoVector Giant Dipole Resonance (IVGDR) in the rare-earth region. Proton inelastic scattering experiments with
E
p
= 200 MeV were performed on the even-even Nd isotope chain and
152
Sm at very forward scattering angles including zero degrees with the K600 magnetic spectrometer. The evolution of the shape of the IVGDR in the transition from spherical to deformed nuclei was investigated. One of the goals of this highlighted study was to confirm the
K
-splitting observed in previous photo-absorption measurements from Saclay. Significant discrepancies were found between the direct (γ, xn) data obtained at Saclay and the equivalent photo-absorption cross sections obtained using (p, p′) data from the K600. Furthermore, discrepancies exist for several nuclei between photo-absorption data taken at the Saclay and Livermore laboratories. These discrepancies, possible reasons for them and future investigations will be presented and discussed.
Differential cross sections of isoscalar and isovector spin-M1 (0(+)→1(+)) transitions are measured using high-energy-resolution proton inelastic scattering at E(p)=295 MeV on (24)Mg, (28)Si, (32)S, ...and (36)Ar at 0°-14°. The squared spin-M1 nuclear transition matrix elements are deduced from the measured differential cross sections by applying empirically determined unit cross sections based on the assumption of isospin symmetry. The ratios of the squared nuclear matrix elements accumulated up to E(x)=16 MeV compared to a shell-model prediction are 1.01(9) for isoscalar and 0.61(6) for isovector spin-M1 transitions, respectively. Thus, no quenching is observed for isoscalar spin-M1 transitions, while the matrix elements for isovector spin-M1 transitions are quenched by an amount comparable with the analogous Gamow-Teller transitions on those target nuclei.
The dipole polarizability of stable even-mass tin isotopes 112,114,116,118,120,124Sn was extracted from inelastic proton scattering experiments at 295MeV under very forward angles performed at RCNP. ...Predictions from energy density functionals cannot account for the present data and the polarizability of 208Pb simultaneously. The evolution of the polarizabilities in neighboring isotopes indicates a kink at 120Sn while all model results show a nearly linear increase with mass number after inclusion of pairing corrections.
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